<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
  <head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
    <title>DbEnv::failchk()</title>
    <link rel="stylesheet" href="apiReference.css" type="text/css" />
    <meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
    <link rel="start" href="index.html" title="Berkeley DB C++ API Reference" />
    <link rel="up" href="env.html" title="Chapter 5.  The DbEnv Handle" />
    <link rel="prev" href="enverr.html" title="DbEnv::err()" />
    <link rel="next" href="envfileid_reset.html" title="DbEnv::fileid_reset()" />
  </head>
  <body>
    <div xmlns="" class="navheader">
      <div class="libver">
        <p>Library Version 11.2.5.3</p>
      </div>
      <table width="100%" summary="Navigation header">
        <tr>
          <th colspan="3" align="center">DbEnv::failchk()</th>
        </tr>
        <tr>
          <td width="20%" align="left"><a accesskey="p" href="enverr.html">Prev</a> </td>
          <th width="60%" align="center">Chapter 5. 
                The DbEnv Handle
        </th>
          <td width="20%" align="right"> <a accesskey="n" href="envfileid_reset.html">Next</a></td>
        </tr>
      </table>
      <hr />
    </div>
    <div class="sect1" lang="en" xml:lang="en">
      <div class="titlepage">
        <div>
          <div>
            <h2 class="title" style="clear: both"><a id="envfailchk"></a>DbEnv::failchk()</h2>
          </div>
        </div>
      </div>
      <pre class="programlisting">#include &lt;db_cxx.h&gt;
 
int
DbEnv::failchk(u_int32_t flags);</pre>
      <p>
         The <code class="methodname">DbEnv::failchk()</code> method checks for threads of control (either a
         true thread or a process) that have exited while manipulating Berkeley
         DB library data structures, while holding a logical database lock, or
         with an unresolved transaction (that is, a transaction that was never
         aborted or committed).  For more information, see 
         <a href="../../programmer_reference/cam_app.html" class="olink">Architecting Data Store and 
         Concurrent Data Store applications</a>, and 
         <a href="../../programmer_reference/transapp_app.html" class="olink">Architecting Transactional 
             Data Store applications</a>, both in the
         <em class="citetitle">Berkeley DB Programmer's Reference Guide</em>.
    </p>
      <p>
         The <code class="methodname">DbEnv::failchk()</code> method is 
         used in conjunction with the 
         <a class="xref" href="envset_thread_count.html" title="DbEnv::set_thread_count()">DbEnv::set_thread_count()</a>,
         <a class="xref" href="envset_isalive.html" title="DbEnv::set_isalive()">DbEnv::set_isalive()</a> and
         <a class="xref" href="envset_thread_id.html" title="DbEnv::set_thread_id()">DbEnv::set_thread_id()</a>
         methods.  Before calling the <code class="methodname">failchk()</code>method, applications must:
     </p>
      <div class="orderedlist">
        <ol type="1">
          <li>
            <p>
                 Configure their database using the 
                <a class="xref" href="envset_thread_count.html" title="DbEnv::set_thread_count()">DbEnv::set_thread_count()</a>
                method.
             </p>
          </li>
          <li>
            <p>
                 Establish an <code class="literal">is_alive()</code> function and
                 invoke
                 <a class="xref" href="envset_isalive.html" title="DbEnv::set_isalive()">DbEnv::set_isalive()</a> 
                 with that function as the <code class="literal">is_alive</code> parameter.
             </p>
          </li>
          <li>
            <p>
                 Establish a <code class="literal">thread_id</code> function and
                 invoke
                <a class="xref" href="envset_thread_id.html" title="DbEnv::set_thread_id()">DbEnv::set_thread_id()</a>
                with that function as the <code class="literal">thread_id</code>
                parameter.
             </p>
          </li>
        </ol>
      </div>
      <p>
         If any of these methods are omitted, a program may be unable to
         allocate a thread control block. This is true of the standalone
         Berkeley DB utility programs. To avoid problems when using the
         standalone Berkeley DB utility programs with environments
         configured for failure checking, incorporate the utility's
         functionality directly in the application, or call the
         <code class="methodname">DbEnv::failchk()</code> method along with its 
         associated methods before running the utility.
     </p>
      <p>
         If <code class="methodname">DbEnv::failchk()</code> determines a thread of control exited while
         holding database read locks, it will release those locks.  If
         <code class="methodname">DbEnv::failchk()</code> determines a thread of control exited with an
         unresolved transaction, the transaction will be aborted.  In either of
         these cases, <code class="methodname">DbEnv::failchk()</code> will return 0 and the application may
         continue to use the database environment.
    </p>
      <p>
         In either of these cases, the <code class="methodname">DbEnv::failchk()</code> method will also
         report the process and thread IDs associated with any released locks
         or aborted transactions.  The information is printed to a specified
         output channel (see the 
         <a class="xref" href="envset_msgfile.html" title="DbEnv::set_msgfile()">DbEnv::set_msgfile()</a> 
         method for more information), or passed to an application callback
         function (see the 
         <a class="xref" href="envset_msgcall.html" title="DbEnv::set_msgcall()">DbEnv::set_msgcall()</a> 
         method for more information).
    </p>
      <p>
         If <code class="methodname">DbEnv::failchk()</code> determines a thread of control has exited such
         that database environment recovery is required, it will return 
         <a href="../../programmer_reference/program_errorret.html#program_errorret.DB_RUNRECOVERY" class="olink">DB_RUNRECOVERY</a>.
         In this case, the application should not continue to use the database
         environment.  For a further description as to the actions the
         application should take when this failure occurs, see 
         <a href="../../programmer_reference/cam_fail.html" class="olink">Handling failure in Data Store and 
         Concurrent Data Store applications</a>, and 
         <a href="../../programmer_reference/transapp_fail.html" class="olink">Handling failure in Transactional Data
             Store applications</a>, both in the
         <em class="citetitle">Berkeley DB Programmer's Reference Guide</em>.
    </p>
      <p>
	In multiprocess applications, it is recommended that the <a class="link" href="env.html" title="Chapter 5.  The DbEnv Handle">DbEnv</a> handle 
        used to invoke the <code class="methodname">DbEnv::failchk()</code> method not be shared and therefore
	not <span class="emphasis"><em>free-threaded</em></span>.  
    </p>
      <p>
             The <code class="methodname">DbEnv::failchk()</code> method may not be called by the 
	     application before the <a class="xref" href="envopen.html" title="DbEnv::open()">DbEnv::open()</a>  
	     method is called.
    </p>
      <p>
         The <code class="methodname">DbEnv::failchk()</code> <span>
            
            <span>
                method either returns a non-zero error value or throws an
                exception that encapsulates a non-zero error value on
                failure, and returns 0 on success.
            </span>
        </span>
    </p>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="idp6751008"></a>Parameters</h3>
            </div>
          </div>
        </div>
        <div class="sect3" lang="en" xml:lang="en">
          <div class="titlepage">
            <div>
              <div>
                <h4 class="title"><a id="idp6750360"></a>flags</h4>
              </div>
            </div>
          </div>
          <p>
                          The <span class="bold"><strong>flags</strong></span> parameter is currently
                          unused, and must be set to 0.
                     </p>
        </div>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="idp6755536"></a>Errors</h3>
            </div>
          </div>
        </div>
        <p>
                         The <code class="methodname">DbEnv::failchk()</code> <span>
            
            <span>
                method may fail and throw a <a class="link" href="dbexception.html" title="Chapter 6. The DbException Class">DbException</a> 
                exception, encapsulating one of the following non-zero errors, or return one
                of the following non-zero errors:
            </span>
        </span>
                    </p>
        <div class="sect3" lang="en" xml:lang="en">
          <div class="titlepage">
            <div>
              <div>
                <h4 class="title"><a id="idp6768072"></a>EINVAL</h4>
              </div>
            </div>
          </div>
          <p>
                An invalid flag value or parameter was specified.
            </p>
        </div>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="idp6766776"></a>Class</h3>
            </div>
          </div>
        </div>
        <p>
                <a class="link" href="env.html" title="Chapter 5.  The DbEnv Handle">DbEnv</a>  
            </p>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="idp6769400"></a>See Also</h3>
            </div>
          </div>
        </div>
        <p>
                     <a class="xref" href="env.html#envlist" title="Database Environments and Related Methods">Database Environments and Related Methods</a> 
                </p>
      </div>
    </div>
    <div class="navfooter">
      <hr />
      <table width="100%" summary="Navigation footer">
        <tr>
          <td width="40%" align="left"><a accesskey="p" href="enverr.html">Prev</a> </td>
          <td width="20%" align="center">
            <a accesskey="u" href="env.html">Up</a>
          </td>
          <td width="40%" align="right"> <a accesskey="n" href="envfileid_reset.html">Next</a></td>
        </tr>
        <tr>
          <td width="40%" align="left" valign="top">DbEnv::err() </td>
          <td width="20%" align="center">
            <a accesskey="h" href="index.html">Home</a>
          </td>
          <td width="40%" align="right" valign="top"> DbEnv::fileid_reset()</td>
        </tr>
      </table>
    </div>
  </body>
</html>
